1. Field of the Invention
The present invention relates generally to a method of making optical fiber ribbons. More particularly, the present invention relates to a method for making an optical fiber ribbon with improved planarity and to an optical fiber ribbon with improved planarity made according to the method.
2. Discussion of Related Art
In optical fiber ribbon, it is desirable to have the individual optical fibers aligned so that the longitudinal axes of the optical fibers are in the same geometric plane. Planarity is important during connection of two ribbon ends. If the two ends have the same planarity, the individual optical fiber ends will be aligned thereby making it easier to establish a connection which will efficiently transmit light.
Existing methods of manufacturing optical fiber ribbon include the use of three dies and two ultraviolet lights to form an optical fiber ribbon. Japanese Patent No. 63-208814 describes such a prior art method. In Japanese Patent No. 63-208814, a precoater applies a thin layer of ribbon matrix material to a plurality of optical fibers. Next, the optical fibers with the thin layer of ribbon matrix material are fed through a primary resin coater where additional matrix material is applied. After passing through the primary resin coater, the matrix material is exposed to ultraviolet light in order to cure the matrix material. Next, the optical fibers with cured matrix material thereon are fed through a secondary coater where additional matrix material is applied to achieve an uncured ribbon. Finally, the matrix material is cured by exposing the matrix material to ultraviolet light to produce an optical fiber ribbon. Using such a method has the disadvantage that the precoater, primary resin coater, and secondary coater must be maintained and checked periodically, resulting in a process which is often shut down for maintenance. In addition, inclusion of the precoater to apply the matrix material has been shown to adversely affect ribbon planarity because the precoater and primary resin coater are almost never properly aligned, thereby making planarity poor.
Another existing method of manufacturing optical fiber ribbon involves the use of a single die having a central opening which is smaller than the exit opening of the die. Japanese Pat. No. 6-63483 describes such a die. In Japanese Pat. No. 6-63483, the optical fibers enter the die through an entrance opening, move to a first coating chamber, through a central opening, to a second coating chamber, and exit the die through the exit opening. Such a die has the disadvantage that the optical fibers can move in the second coating chamber, the exit section and after leaving the die until the matrix material is set, for example through curing of the matrix material. As a result, it is very difficult to use such a die to produce an optical fiber ribbon in which the optical fibers are arranged in a plane.